1. Field of the Invention
This invention relates to a battery charging condition detecting method for accurately detecting a dischargeable or residual capacity of a battery or a degree of deterioration of the same.
2. Prior Art
Of some related prior arts, the unexamined Japanese patent application No. 52-79234/1977 discloses a system for detecting a battery voltage when a discharge current is constant, and converting the detected voltage into a corresponding battery capacity (i.e. dischargeable capacity) which is displayed in terms of a residual percentage of battery capacity.
The unexamined Japanese patent application No. 1-288784/1989 discloses a system for calculating a residual capacity (i.e. dischargeable capacity) by accumulating momently discharged amounts of a battery and correcting the accumulated value in accordance with a battery voltage or a specific gravity of battery electrolyte, thereby obtaining an accurate residual capacity.
The former system, disclosed in the unexamined Japanese patent application No. 52-79234/1977, is not satisfactory simply because it merely detects a relative percentage (to be estimated based on the detected battery voltage) which is explicitly inferior to the absolute value of the residual battery capacity directly measured or calculated. Such a system cannot be practically employed in an electric motor vehicle or the like which generally subject the battery to severe conditions, such as long-lasting and frequently repeated charging and discharge operations that could possibly cause charging polarizations in a battery, accompanied by an uncontrollable change in the relationship between the battery voltage and the battery capacity.
On the other hand, the latter system disclosed in the unexamined Japanese patent application No. 1-288784/1989 is able to quantitatively detect the residual capacity. However, performing correction of the residual capacity in accordance with the battery voltage or the specific gravity of battery electrolyte is basically troublesome since accuracy of measurement is greatly affected by various factors, such as temperature and charging/discharging conditions, thus possibly resulting in an erroneous measurement.